• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.7
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• pp.751-757
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• 2012

An accelerated life test (ALT) is a test method that forces components to fail more quickly than they would under use conditions by applying higher overstresses. When two or more accelerating stresses are involved in an ALT, an interaction effect may occur. In previous studies, mostly ALTs without considering an interaction of accelerated stresses and accelerated life models were proposed. The life data obtained are extrapolated using a life-stress relationship to estimate the life distribution at use conditions. We use the general log-linear relationship to model the dependence of life in the Weibull distribution on stress. Therefore, this study suggests the acceleration factor model between the lives at use conditions and accelerated conditions by using mechanical component life data considering an interaction effect. Further, the accelerated life test method and acceleration factor model proposed in this paper will be the basis for adopting an accelerated life test with accelerated stress interactions.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.41-55
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• 2003

A dynamically-interfaced multi-grid finite difference model for simulation of tsunamis in the East Sea(Choi et al.) was established and further applied to produce detailed feature of coastal inundations along the whole eastern coast of Korea. The computational domain is composed of several sub-regions with different grid sizes connected in parallel of inclined directions with 16 innermost nested models. The innermost sub-region represents the coastal alignment reasonably well and has a grid size of about 30 meters. Numerical simulations have been performed in the framework of shallow-water equations(linear, as well as nonlinear) over the plane or spherical coordinate system, depending on the dimensions of the sub-region. Results of simulations show the general agreements with the observed data of run-up height for both tsunamis. The evolution of the distribution function of tsunami heights is studied numerically and it is shown that it tends to the log-normal curve for long distance from the source.

• Journal of Preventive Medicine and Public Health
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• v.33 no.1
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• pp.31-35
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• 2000

Objectives : This study aimed to estimate the completeness of cancer registration with Capture-recapture method. Methods : The study was conducted in the population based cancer registry of Kwangju, Korea, for which there are three main sources of notification: reports by Korean Central Cancer Registry, reports by pathology data, and the others reports by radiology data, death certificates, etc. The defined cases in three sources were matched by 13 digits Resident Register Number. To derive an estimates, log-linear models were applicated. Results : Overall completeness was estimated to be around 93%. There was some variation with age(consistently high levels below age group 60-74 years, a minimum of 88.6% above 75 years). Among the most common cancer sites, estimates of completeness were highest for thyroid cancer(97.1%), while lower estimates of completeness were derived for stomach cancer(92.3%), liver cancer(92.6%). Conclusions : Careful application of Capture-recapture method may provide an alternative to traditional approaches for estimating the completeness of cancer registration in Kwangju city.

• Korean Journal of Ecology and Environment
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• v.44 no.2
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• pp.214-225
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• 2011

The objectives of the study were to evaluate seasonal patterns of epilimnetic water quality, and determine interannual eutrophication patterns at the dam site of Yong-dam Reservoir using long-term data during 2002~2009. Ionic dilutions, based on specific conductivity, occurred in the summer period in response to the intense monsoon rain and inflow, and suspended solid analysis indicated that the reservoir was clear except for the monsoon. Seasonality of nitrogen contents varied depending on the types of nitrogen and responded to ionic dilution; Ammonia-nitrogen ($NH_4$-N) peaked at dry season but nitrate-nitrogen ($NO_3$-N) peaked in the monsoon when the ionic dilution occurred. The maxima of $NO_3$-N seemed to be related with external summer N-loading from the watershed and active nitrogen fixation of bluregreens in the summer. $NO_3$-N was major determinant (>50%) of the total nitrogen pool and relative proportion of $NH_4$-N was minor. Long-term annual $NO_3$-N and TDN showed continuous increasing trends from 2004 to 2009, whereas TP and TDP showed decreasing trends along with chlorophyll-a (CHL) values. Empirical model analysis of log-transformed nutrients and N : P ratios on the CHL showed that the reservoir CHL had a stronger linear function with TP ($R^2$=0.89, p<0.001) than TN ($R^2$=0.35, p=0.120). Overall results suggest that eutrophication progress, based on TP and CHL, is slow down over the study period and this was mainly due to reduced phosphorns, which is considered as primary nutrient by the empirical model.

• The Korean Journal of Applied Statistics
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• v.34 no.3
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• pp.411-425
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• 2021

Accelerated failure time (AFT) model represents a linear relationship between the log-survival time and covariates. We are interested in the inference of covariate's effect affecting the variation of survival times in the AFT model. Thus, we need to model the variance as well as the mean of survival times. We call the resulting model mean and variance AFT (MV-AFT) model. In this paper, we propose a variable selection procedure of regression parameters of mean and variance in MV-AFT model using penalized likelihood function. For the variable selection, we study four penalty functions, i.e. least absolute shrinkage and selection operator (LASSO), adaptive lasso (ALASSO), smoothly clipped absolute deviation (SCAD) and hierarchical likelihood (HL). With this procedure we can select important covariates and estimate the regression parameters at the same time. The performance of the proposed method is evaluated using simulation studies. The proposed method is illustrated with a clinical example dataset.

• Clinical and Experimental Reproductive Medicine
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• v.48 no.2
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• pp.163-173
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• 2021

Objective: This study aimed to characterize a validated model for predicting oocyte retrieval in controlled ovarian stimulation (COS) and to construct model-based nomograms for assistance in clinical decision-making regarding the gonadotropin protocol and dose. Methods: This observational, retrospective, cohort study included 636 women with primary unexplained infertility and a normal menstrual cycle who were attempting assisted reproductive therapy for the first time. The enrolled women were split into an index group (n=497) for model building and a validation group (n=139). The primary outcome was absolute oocyte count. The dose-response relationship was tested using modified Poisson, negative binomial, hybrid Poisson-E_max, and linear models. The validation group was similarly analyzed, and its results were compared to that of the index group. Results: The Poisson model with the log-link function demonstrated superior predictive performance and precision (Akaike information criterion, 2,704; λ=8.27; relative standard error (λ)=2.02%). The covariate analysis included women's age (p<0.001), antral follicle count (p<0.001), basal follicle-stimulating hormone level (p<0.001), gonadotropin dose (p=0.042), and protocol type (p=0.002 and p<0.001 for short and antagonist protocols, respectively). The estimates from 500 bootstrap samples were close to those of the original model. The validation group showed model assessment metrics comparable to the index model. Based on the fitted model, a static nomogram was built to improve visualization. In addition, a dynamic electronic tool was created for convenience of use. Conclusion: Based on our validated model, nomograms were constructed to help clinicians individualize the stimulation protocol and gonadotropin doses in COS cycles.

• Korean Journal of Soil Science and Fertilizer
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• v.33 no.6
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• pp.398-404
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• 2000

We examined the effect of soil:water ratio on the equivalent concentration of individual electrolyte species and the electrical conductivities (EC) of the diluted extracts of 24 soil samples (loam or silt loam) collected from rose-cultivated plastic houses to estimate the EC of saturated soil-paste extracts (ECe) from diluted soil extracts. With increasing volume ratio of water (higher dilution), the equivalent concentrations of each electrolyte species and their sum increased. The relative contribution to the EC, however, was highest for $NO_3{^-}$, irrespective of soil:water ratio. The measured ECe was 6.36 for loam and $8.09dS\;m^{-1}$ for silt loam soils and the corresponding soil:water ratio was 0.38 and 0.50, respectively. The EC_e estimated from the EC of diluted extracts at 1:1, 1:2, or 1:5 soil:water ratios using their corresponding uniform diluted factors was lower than the measured EC_e and this difference was greater with higher dilution and EC values. Therefore, the alternative diluted factors (y) for each soil: water ratio were obtained following the definition of diluted factor and were correlated significantly with volume ratios of added water (x): y=1.55x+0.5 for loam and y=1.21x+0.48 for silt loam soils. On the other hand, correlation analyses of the EC of soil extracts (y) to the volume ratio of added water (x) on log-log scale yielded linear models: logy = -0.805logx + logb, SD of slope=0.05, b=sample specific constant, n=24). With known saturation percentage of a sample representing a group and and the EC of diluted extract of a given soil, the EC_e could be predicted using the proposed logarithmic equation.

• Journal of Korean Society of Forest Science
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• v.85 no.3
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• pp.453-461
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• 1996

Three Phyllostachys stands of P. pubescens, P. bambusoides and P. nigra var, henonis in Sunchon were studied to investigate biomass, net production and nutrient distribution. Five $10m{\times}10m$ quadrats were set up and 20 sample culms of 2 years and over were harvested for dimension analysis in each stand. One year old culms and subterranean parts were estimated by the harvested quadrat method. The largest mean DBH, height and basal area were shown in P. pubescens stand, and followed by P. nigra var. henonis stand and P. bambusoides stand. There was little difference in accuracy among three allometric biomass regression models of logWt=A+B1ogD, $logWt=A+BlogD^2H$ and logWt=A+BlogD+ClogH, where Wt, D and H were dry weight, DBH and height, respectively. Analysis of covariance showed that there were significant differences in intercept among the linear allometric biomass regressons of three Phyllostachys species. Biomass included subterranean parts was the largest in P. pubescens stand(103.621t/ha), and followed by P. nigra var. henonis stand(86.447t/ha) and P. bambusoides stand(36.767t/ha). Leaf biomass was 6.3% to 7.8% of total biomass in each stands. The ratio of aboveground biomass and subterranean biomass in each stand was 1.87 to 2.26. Net production included subterranean parts was the greatest in P. pubescens stand(6.115t/ha/yr), and followed by P. nigra var. henonis stand(5.609t/ha/yr) and P, bambusoides stand(3.252t/ha/yr). The highest net assimilation ratio was estimated in P. pubescens stand(2.979), and followed by P. nigra var. henonis stand(2.752) and P. bambusoides stand(2.187). Biomass accumulation ratio of each stand was 2.679 to 5.358. Concentrations of N, P and Mg were the highest in leaves, and followed by subterranean parts, and culms+branches in all three species. Concentration of Ca was the highest in leaves, and followed by culms+branches, and subterranean parts in all three species. The difference in biomass among three species stands was caused by their culm size, leaf biomass, net assimilation ratio, and efficiency of leaves to produce culms.

• Korea journal of population studies
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• v.25 no.1
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• pp.33-50
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• 2002

This study examines cross-national patterns of asymmetry of marriage tables with respect to educational level and tries to measure the degree of gender inequality across nations. A Primary assumption of the study is that gender inequality inhibits symmetric marriage between men and women. As men and women differ more in status, the rate of symmetric marriage between them declines thus producing asymmetric marriage with respect to social status. More specifically, the main object of the study is to develop statistical models and index with which to assess the patterns and degree of asymmetric marriage. Additionally, it is intended to assess the appropriateness of several theoretical perspectives for explaining these variations identified by the statistical models. Two most important such perspectives are industrialism and theory of politics and culture. To answer these questions, this study relies on twenty-seven marriage tables with respect to educational level, some from published tables, and some extracted from other sources. The main findings of the study are: (1) compared to less industrialized countries, more industrialized countries have lower degrees of asymmetric marriage(gender inequality) with respect to educational level, and (2) other things being equal, differences in politics and culture seem to have the some impact on marriage pattern; for instance, social democracy and state socialism reduce the degree of asymmetric marriage while the high emphasis on gender-based hierarchy in Asian countries seems to increase it In short, these results suggest a weaker or modified version of industrialists That is, while with economic growth most nations show a decline in the degrees of asymmetric marriage with respect to social status, for some nations the degrees of asymmetric marriage are affected by their specific politics or cultures.

• Korean Journal of Ecology and Environment
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• v.45 no.4
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• pp.378-391
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• 2012

The objective of this study was to determine temporal patterns and longitudinal gradients of water chemistry at eight artificial reservoirs and ten streams within the Han-River watershed along the main axis of the headwaters to the downstreams during 2009~2010. Also, we evaluated chemical relations and their variations among major trophic variables such as total nitrogen (TN), total phosphorus (TP), and chlorophyll-a (CHL-a) and determined intense summer monsoon and annual precipitation effects on algal growth using empirical regression model. Stream water quality of TN, TP, and other parameters degradated toward the downstreams, and especially was largely impacted by point-sources of wastewater disposal plants near Jungrang Stream. In contrast, summer river runoff and rainwater improved the stream water quality of TP, TN, and ionic contents, measured as conductivity (EC) in the downstream reach. Empirical linear regression models of log-transformed CHL-a against log-transformed TN, TP, and TN : TP mass ratios in five reservoirs indicated that the variation of TP accounted 33.8% ($R^2$=0.338, p<0.001, slope=0.710) in the variation of CHL and the variation of TN accounted only 21.4% ($R^2$=0.214, p<0.001) in the CHL-a. Overall, our study suggests that, primary productions, estimated as CHL-a, were more determined by ambient phosphorus loading rather than nitrogen in the lentic systems of artificial reservoirs, and the stream water quality as lotic ecosystems were more influenced by a point-source locations of tributary streams and intense seasonal rainfall rather than a presence of artificial dam reservoirs along the main axis of the watershed.